3x+5y=9
3x-y=-7
solve using subtraction
3x+5y = 9 ...(1)
3x - y = -7 ...(2)
Subtract (2) from (1) term by term:
3x-3x + 5y-(-y) = 9 - (-7)
6y = 16
y = 16/6 = 8/3
Rearrange (2) to get x = (y-7)/3 or x = (8/3-7)/3 or x = -13/9
